Stimulated release of hypothalamic growth hormone-releasing activity by morphine and pentobarbital

Two minutes after the intravenous administration of 1 ml of sheep somatostatin antiserum in the rat, plasma growth hormone (GH) levels had reached a maximal 10-15-fold increase which remained approximately constant up to 90 min. The injection of sodium pentobarbital (2 mg/100 g body wt) led to a rapid and transient rise of plasma GH levels of similar magnitude (10-fold) reached 20 to 40 min after injection of the narcotic. The important finding is, however, that the combined administration of somatostatin antiserum and pentobarbital or morphine led to an almost exact additive effect on the plasma GH concentrations. These data, beside providing additional evidence for the existence of GH-releasing activity (GH-RH), indicate that morphine and pentobarbital stimulate GH secretion through increased release of GH-RH.